This invention relates to a method of gas purification and a system therefor. More particularly, the invention relates to a method and device for gettering impurities such as oxygen, nitrogen and water from inert gases such as cover gases employed in a glove box.
It is known that reactive metals at elevated temperatures react readily with atmospheric gases, particularly oxygen and to some extent nitrogen, as well as with water. This characteristic has enabled them to be employed as so-called getters. In the prior art, it is also known that inert gases such as helium and argon often have trace amounts of, e.g., oxygen, nitrogen and water, and it is often required that they be purified by removal of as much as possible of their impurity content. Treatment of such gases with a reactive metal getter has therefore proved to be a convenient way of conducting the purification process.
Gettering devices generally have employed a body of reactive metal, such as titanium or zirconium sponge which is maintained at an elevated temperature of between, e.g., 800.degree. and 1000.degree. C. Typically, the gas to be purified is passed in contact with the reactive metal at this temperature. However, these systems have a disadvantage in that breakdowns in the operation of the gettering device tend to occur more readily at higher operational temperatures, and the effects of such breakdowns are greatly magnified as a result of the higher temperatures.
One such prior art device is, for example, disclosed in U.S. Pat. No. 3,273,970 to Priscu et al. which discusses the use of a reactive metal in a gettering device maintained at an elevated temperature of 800.degree.-1000.degree. C. In this device, the reactive metal getter is maintained in the molten state and the gas is brought in contact with the heated molten metal getter to effect purification thereof.
In an unrelated development, various light weight metal alloys have been prepared in the prior art which have high melting points, are ductile, maleable, machinable, and structurally strong. Typically, prior to the development of these alloys beryllium was previously used because it met many of these requirements, but by nature because it was too brittle and toxic, it created a number of problems in its use. One alloy proposed as a substitute was the recently developed lithium-boron alloys, the preparation of which is disclosed in U.S. Pat. No. 4,110,111 to Wang, whose disclosure is incorporated by reference herein.
It is also known from Boron and Refractory Borides, V. I. Matkovich, Page 268, Springer-Verlag, Berlin, Heidelberg, New York (1977), that although there is agreement about the existence, within the lithium-boron system of one or several phases, there is wide variation in the Li/B ratios from chemical analysis depending on the method of preparation. Thus, although it is possible to prepare such systems, it is not always possible to give precise formulas from elementary analysis alone.
According to S. Dallek, D. W. Ernst and B. F. Larrick, Thermal Analysis of Lithium-Boron Alloys, J. Electrochem. Society, 126, 6 (1979), it is known to use these lithium boron and other related alloys such as LiAl and LiSi systems in voltaic cells as anode materials. However, in use as an anode material it was found that these alloys, especially the lithium-boron compounds, are extremely reactive with components of the atmosphere.